1. Technical Field
The present invention relates generally to sprayer apparatus, and, more particularly to backpack or knapsack sprayers employing a pressure vessel or accumulator to produce a pressure source for discharging fluid at the spray nozzle.
2. Background Art
A conventional backpack sprayer includes a supply tank which is normally dimensioned to hold between two and five gallons of liquid, a manual lever pump, a pressure vessel or accumulator, a manual shut-off valve, and a spray wand with a nozzle. In operation, the pump draws discharge liquid from the supply tank and pumps it into the accumulator. Initially, the accumulator contains air at atmospheric pressure. As liquid is pumped into the accumulator, normally from its bottom, the air inside is compressed at the top of the vessel. The compressed air acts as a spring on the liquid and provides a pressure source for discharging the liquid. Once the liquid is discharged from the accumulator it is directed to a spray nozzle to effectuate a desired spray pattern. An example of a conventional backpack sprayer is one manufactured by D. B. Smith & Co., Inc., Utica, N.Y., under the brand name of FIELD KING.RTM. In addition, conventional backpack sprayers are described in U.S. Pat. No. 5,335,853 to Wirz and U.S. Pat. No. 2,162,057 to Brandt et al.
In the operation of a conventional pressure vessel or accumulator, energy is stored in the compressed air until the liquid is allowed to be discharged from the accumulator. This method of storing energy is very inefficient because the air is heated when it is compressed. This heat is energy lost that cannot be recovered. The efficiency of the accumulator directly affects the utility of the sprayer. As the efficiency of the accumulator increases, the number of pump strokes necessary to produce a desired discharge pressure is decreases. Thus, an inefficient accumulator relates to operator fatigue and reduces the utility of the sprayer for many applications.
In a conventional compressed-air accumulator, the pressure exerted on the liquid does not remain constant as the volume of the liquid in the accumulator changes. This characteristic creates several problems. First, a higher accumulator pressure is required to achieve a given spray duration than would be necessary if the pressure source were constant. The higher the pressure, the more inefficient a fixed volume accumulator becomes. Thus, for long duration spray applications, the conventional backpack sprayer becomes very inefficient.
Second, a fixed volume accumulator produces a continuously decreasing discharge pressure as the liquid therein is being expelled. This results in non-uniform application of the liquid being sprayed. This performance is especially undesirable when chemicals, such as insecticides, herbicides or fungicides, are being sprayed. In many cases, non-uniform application leads to reapplication, and thus overuse and waste of the chemicals being sprayed.
Third, when the application requires a constant spray rate, a pressure regulator must be used with a conventional backpack sprayer. This component is relatively expensive considering the overall cost of a conventional backpack sprayer. The pressure regulator also reduces the efficiency of the sprayer.
All of these problems that are associated with a conventional backpack sprayers have existed for nearly 100 hundred years. Heretofore, no satisfactory solution to these problems have been proposed. The present invention has finally solved these long standing problems, and has accomplished this achievement by a simple and inexpensive modification to the conventional backpack sprayer design.